Perhaps I should have been clearer, but I never said trains could be diverted - just the passengers.
I fully realise (and lament, in an old-fogey, BR way) modern railway managements' huge difficulty, if not total unwillingness, to actually divert real trains across alternative routes.
The problem is the network is much more intensively used than it was in the 60s and 70s. Look at the GW diversions over Christmas / New Year as an example. 30 years ago Banbury - Marylebone and Exeter - Basingstoke were at best hourly services. Plenty of room for slotting in additional services. Now the picture is quite different - Chiltern and SW Trains both had to cancel services to create paths for the GW diversions to use.
The other - relevant - example that was used in the 80s - diverting WCML services via Bedford and onto St Pancras. Again, back then the MML had far less traffic of its own and St Pancras was a vast, under-used terminus. Now, there are pretty much no free slots between Bedford and London - and St Pancras is running at capacity.
That's the reality of the situation - nothing to do with 'privatisation' or 'fragmentation' of the railway - everything to do with the volume of traffic now being handled.
Some diversions are still used - e.g. on the ECML diverts happen via Lincoln and via Cambridge when necessary, but these again have to pathed around existing demand.
[I think stock clearance and crew training for such eventualities should be in the franchise agreements, eg Virgin WC should be compelled to train up for, and use, the S&C for diversions when the Shap route is closed, whereas it seems it is merely an option, and they prefer to bustitute.]
But there are two problems there - one the S&C doesn't serve the places en-route so between Preston and Carlisle, you can't serve any of the WCML's intermediate stations - one good reason to provide a coach substitute.
Secondly, the S&C has long signal blocks and therefore limited capacity. Add to that a low linespeed and you're actually adding more of a time penalty than using the coach option.
People wanting to travel from London - Scotland in those circumstances are better off travelling from Kings Cross. Ditto from the Midlands - use XC services to Edinburgh if they really don't want to use a rail replacement coach.
But back to EW rail. Yes, I meant de-train. nonetheless, if the WCML is closed for planned PW work, once EW is up and running, specially enhanced services could be run between Marlybone and Bletchley or MK to plug that gap at weekends. Much better than buses, surely?
Again - it depends. If they want to travel to the intermediate stations between MKC and London then diverting via Chiltern is no good. Similarly, the Chiltern route is generally busy (both in terms of number of people on the trains and capacity on the line). You try handling a couple of Pendo's worth of passengers onto a 3 car DMU from Aylesbury to Marylebone in addition to the people already planning to travel on that route and you've got a recipe for overcrowding and far more frustrated passengers than if you'd just put those from MK onto a coach.
